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[222.152.189.137]) by smtp.gmail.com with ESMTPSA id b5sm11515267pgh.41.2021.06.20.20.36.43 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 20 Jun 2021 20:36:52 -0700 (PDT) Subject: Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch_stack To: Al Viro References: <924ec53c-2fd9-2e1c-bbb1-3fda49809be4@gmail.com> <87eed4v2dc.fsf@disp2133> <5929e116-fa61-b211-342a-c706dcb834ca@gmail.com> <87fsxjorgs.fsf@disp2133> <87zgvqor7d.fsf_-_@disp2133> <87mtrpg47k.fsf@disp2133> <87pmwlek8d.fsf_-_@disp2133> <87k0mtek4n.fsf_-_@disp2133> <393c37de-5edf-effc-3d06-d7e63f34a317@gmail.com> Cc: "Eric W. Biederman" , Linus Torvalds , linux-arch , Jens Axboe , Oleg Nesterov , Linux Kernel Mailing List , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Geert Uytterhoeven , linux-m68k , Arnd Bergmann , Ley Foon Tan , Tejun Heo , Kees Cook From: Michael Schmitz Message-ID: <9db8096e-677f-3852-6ca4-28143a228ec3@gmail.com> Date: Mon, 21 Jun 2021 15:36:41 +1200 User-Agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Icedove/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Al, Am 21.06.2021 um 14:27 schrieb Al Viro: > On Mon, Jun 21, 2021 at 02:01:18PM +1200, Michael Schmitz wrote: >> Hi Eric, >> >> instrumenting get_reg on m68k and using a similar patch to yours to warn >> when unsaved registers are accessed on the switch stack, I get a hit from >> getegid and getegid32, just by running a simple ptrace on ls. >> >> Going to wack those two moles now ... > > Explain, please. get_reg() is called by tracer; whose state are you checking? The check is only triggered when syscall tracing (I set a flag on trace entry, and clear that on trace exit)... From the WARN_ONCE stack dump, it appears that I get the warning from inside the syscall, not syscall_trace(). > Because you are *not* accessing the switch stack of the caller of get_reg(). > And tracee should be in something like syscall_trace() or do_notify_resume(); > both have SAVE_SWITCH_STACK done by the glue... And that's where my problem may be - I stupidly forgot to set the 'all registers saved' flag before calling syscall_trace() ... I'll fix that and try again. Sorry for the noise! Cheers, Michael >